Note: ver 56.0.2 is no longer receiving any updates and is now listed as a Security Risk. Use 52.4.0 ESR or return to 57+ and ask questions before jump to action. This usually leads to more work for both sides to uncover the issue. Note jumping back and forth is sure to screw up your Profile with all your info in it as not compatible. uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files and C:\Program Files(x86) Then restart system. Then run Windows Disk Cleanup. Then run it again and click the button that says Cleanup System Files. Note: your Firefox Profile is saved. But you should make a back up before you do : https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer do this often and overwrite, save in multiple places, mine are from 95 Reinstall with Current Release Firefox 57.0.2 with a Full Version Installer https://www.mozilla.org/firefox/all/ Please let us know if this solved your issue or if need further assistance.